Studies will be conducted on sterol and steryl ester metabolism in tissue culture cells. The mechanism of cholesterol feedback will be investigated and related to cellular sterol flux. The regulation of sterol influx and efflux by serum lipoproteins will be determined using purified serum lipoproteins. The role of sterols in cellular membranes will be investigated using sterol-deficient cells and the sterol delta 24-reductase will be assayed in both cholesterol and desmosterol synthesizing cells.